In a packaging operation a horizontal conveyor belt extends in a longitudinal travel direction through a filling machine and then through a capping machine. A longitudinal row of upwardly open vessels sitting on the belt is stepped through the two machines. In the filling machine each vessel is filled with whatever material, a foodstuff for instance, that it is to contain. In the capping machine the cover is applied to the top of the filled vessel. Other machines downstream of the capper can seal the package thus formed and label it while upstream of the filling machine other devices are loading the vessels onto the belt and otherwise preparing them for filling.
This capping machine normally holds a stack of upside-down caps or covers. A suction-type gripper or the like is carried on a shaft that extends horizontally perpendicular to the transport direction. The shaft can be moved angularly, that is rotated, about its axis to move the gripper in an arc centered on the shaft axis and can be moved perpendicular to this direction, translatory movement.
Synchronously with the stepwise advance of the vessels through the capping machine the shaft is moved up to press the gripper up against the lowermost cover in the supply stack and adhere it thereto. Then the shaft is lowered to pull the gripper down and free this lowermost cover from the stack and at the same time the shaft rotates to move the gripper through a 180.degree. arc and position the cap right-side-up over the vessel underneath it in the capping station. The shaft and gripper are then moved down to fit the cover to the vessel. Thereafter the capped vessel is moved away while the gripper reverses, moving up and inverting to start the cycle over again.
This combined rotation/translation of the shaft carrying the gripper necessitates a fairly complex drive system which must work at relatively high speed in a standard mass-production packaging operation. In a multiline system where several parallel rows of vessels are stepped simultaneously through the filling and capping machines the assembly of the shaft with its grippers becomes somewhat massive, complicating the problem of moving it accurately and rapidly.
In German Pat. No. 3,111,896 the shaft carrying the gripper shaft is journaled in a vertically displaceable frame and is provided on one end with a wheel. A vertical row of bumps on a stationary support or guide can engage in a corresponding row of hollows in the rim of the wheel and rotate it as the frame moves up and down, the wheel diameter being such that the vertical stroke of the frame is about equal to one-half of its circumference. In the side of the wheel rim opposite the row of recesses there is a guide groove extending radially of the shaft. A lower cam and a central cam can fit into this groove as it moves up and down. Thus with each vertical displacement of the frame the shaft is rotated through 180.degree.. The problem with this arrangement is that it operates in a very jerky manner and is quite noisy, especially when operating at high speed.
Another arrangement described in German patent document No. 3,037,455 has a shaft that can rotate and be vertically reciprocated, and that carries for each of several parallel rows of vessels to be capped a holder having several arms projecting radially from the shaft and each carrying a respective cap gripper. A separate vertically effective actuator is needed to move such a massive shaft assembly up and down. In addition the pneumatic control of the various grippers necessitates complex valve equipment and considerable pump capacity. As a result this type of unit is a frequent service problem.